How do I stay objective when I want my theory to be right?

You feel the pull of your own hypothesis, and the incentives that reward you for being right rather than for being honest. That pull is human, and noticing it is the first real defense against it. The dangerous scientists are the ones who don't feel it. The whole worth of your work rests on one thing: that you followed the evidence even when it wounded your pride. A result bent to fit your hopes isn't knowledge; it's a wish in a lab coat. The discipline to let the data overrule you is the hardest and most valuable thing you own. Build a habit that makes honesty easier than self-deception. Write down what would prove you wrong before you look, and take that test seriously. If you're willing to name your own exit, you're already most of the way to the truth.